Our long term goal is to define mechanisms regulating generation of peripheral and central neurons from dividing precursors. Previously, we found that epigenetic factors regulate proliferation in a population- specific fashion, increasing precursor mitosis and survival. While evidence suggests that local factors control neurogenesis, our current studies indicate that distant signals also influence proliferation: 1) Dividing precursors in culture and in vivo possess "paramitotic" neurites, through which target-derived signals alter mitosis and survival; 2) Peripheral injection of bFGF stimulates brain neurogenesis, crossing rapidly the blood-brain barrier (BBB). Thus distant target signals, acting via paramitotic processes or across the BBB, may serve to coordinate body and brain growth. We will define the effects of distant signals in culture and in vivo, examining neurogenesis during ontogeny and maturity. Specifically, we will define (a) axodendritic identity and developmental expression of sympathetic neuroblast paramitotic processes, (b) paramitotic processes and target regulation and expression of cerebellar granule paramitotic processes, (d) kinetics and selectivity of peripheral bFGF transport across the BBB, (e) fate of bFGF-responsive cells in developing and mature brain, and (f) ontogenic and reparative functions of bFGF-induced neurogenesis. Our strategy employs neuronal precursors from embryonic sympathetic ganglia and postnatal brain, including cerebellum, hippocampus, olfactory bulb, and subventricular zone. Mitotic cells are assessed by incorporation of [3H] thymidine and BrdU. Cell survival, neurite outgrowth, and division are assayed by microscopy, retrograde axonal tracing, and time-lapse analysis. Cell death will be assayed by TUNEL and DNA fragmentation. Neural fate and axodendritic characters of mitotic precursors is defined by immuno-colocalization of BrdU and neuroglial antigens. Kinetics of bFGF transport into brain and CSF is detected using spectroscopy of 125I-bFGF and RIA of unlabeled factor. Long term neurogenetic effects of peripheral bFGF will be assessed biochemically and morphologically, during ontogeny and maturity, and after brain damage. By defining target and somatic regulation of proliferation, we may gain insight into mechanisms of normal ontogeny, providing new pathogenetic models. Further, we may design therapies, such as peripheral bFGF, to redress neuronal deficiencies associated with congenital, degenerative, and acquired brain disease.